Of the hormones involved in the reproductive functions of the male, the steroid testosterone represents the singularly most important hormone reponsible for the differentiation and manifestation of adult male sexual characteristics. The mechanism of testosterone (androgen) action in eliciting these effects is one of the important aspects in our understanding of reproductive development and constitutes the main objective of this proposed project. The approach to the proposed research is based on the concept that the primary hormonal action is gene activation and on the observations that steroid hormonal action proceeds by an initial binding of the hormone to a cytosol receptor molecule in the target tissue, with subsequent transfer of the hormone to the nucleus and chromatin. Experiments are designed to investigate androgen binding to nuclear and chromatin proteins, to isolate and purify the androgen-binding chromatin proteins or androgen acceptors, to document androgen-induced alteration in chromatin and to demonstrate that androgen binding to prostate chromatin leads directly to gene activation. Prostate from castrated rat will be used as the target tissue and androgen-cytosol receptor complex, isolated either by injection in vivo of testosterone to rats or by incubation of minced prostate with the hormone, will be used to effect binding of androgens to nuclear or chromatin acceptors. Template activity of and RNA transcribed from androgen bound prostatic chromatin will be determined to ascertain gene activation, and changes in chromosomal proteins affected by testosterone administration as an indication of altered chromatin. The data from the above studies will give evidence in support of gene action as androgen action and further our understanding of the basic operations involved in reproductive physiology.